The organic and mineral components in two coals and resulting high-temperature ashes with high silicon content were characterized by second-derivative infrared spectroscopy, Raman spectroscopy, and X-ray diffraction (XRD). The infrared spectra of raw coals show weak organic functional groups bands but strong kaolinite bands because of the relatively high silicates content. In contrast, the Raman spectra of raw coals show strong disordered carbon bands but no mineral bands since Raman spectroscopy is highly sensitive to carbonaceous phases. The overlapping bands of mineral components (e.g., calcite, feldspar, and muscovite) were successfully resolved by the method of second-derivative infrared spectroscopy. The results of infrared spectra indicate the presence of metakaolinite in coal ashes, suggesting the thermal transformation of kaolinite during ashing. Intense quartz bands were shown in both infrared and Raman spectra of coal ashes. In addition, Raman spectra of coal ashes show a very strong characteristic band of anatase (149 cm–1), although the titanium oxides content is very low. Combined use of second-derivative infrared spectroscopy and Raman spectroscopy provides valuable insight into the analyses of mineralogical composition. The XRD results generally agree with those of FTIR and Raman spectroscopic analyses.
Two waste biomass materials, pine needle (PN) and corn stalk (CS), were pyrolyzed at different temperatures (200–900 °C). The organic functional groups and carbonaceous structure of the biomass chars were characterized by Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy, respectively. The combustion characteristics and kinetics of biomass chars were investigated by thermogravimetric analysis (TGA). The content of carbon-, hydrogen-, and oxygen-containing functional groups in the biomass samples decreases with an increase in preparation temperature, leading to more aromatic macromolecular structure at elevated pyrolysis temperatures. With increasing pyrolysis temperature, the comprehensive combustibility index (S) of both chars related to combustion reactivity generally decreases especially for CS char because of the loss of active groups. However, the Raman spectra show that the degree of order decreases with increasing pyrolysis temperature from 400 to 700 °C because of the generation of isolated sp2 carbon.
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